Inkjet printing mechanisms use cartridges, often called "pens," which eject drops of liquid colorant, referred to generally herein as "ink," onto a page. Each pen has a printhead formed with very small nozzles through which the ink drops are fired. To print an image, the printhead is propelled back and forth across the page, ejecting drops of ink in a desired pattern as it moves. The particular ink ejection mechanism within the printhead may take on a variety of different forms known to those skilled in the art, such as those using piezo-electric or thermal printhead technology. For instance, two earlier thermal ink ejection mechanisms are shown in U.S. Pat. Nos. 5,278,584 and 4,683,481. In a thermal system, a barrier layer containing ink channels and vaporization chambers is located between a nozzle orifice plate and a substrate layer. This substrate layer typically contains linear arrays of heater elements, such as resistors, which are energized to heat ink within the vaporization chambers. Upon heating, an ink droplet is ejected from a nozzle associated with the energized resistor. By selectively energizing the resistors as the printhead moves across the page, the ink is expelled in a pattern on the print media to form a desired image (e.g., picture, chart or text).
To clean and protect the printhead, typically a "service station" mechanism is supported by the printer chassis so the printhead can be moved over the station for maintenance. For storage, or during non-printing periods, the service stations usually include a capping system which substantially seals the printhead nozzles from contaminants and drying. Some caps are also designed to facilitate priming, such as by being connected to a pumping unit that draws a vacuum on the printhead. During operation, clogs in the printhead are periodically cleared by firing a number of drops of ink through each of the nozzles in a process known as "spitting," with the waste ink being collected in a "spittoon" reservoir portion of the service station. After spitting, uncapping, or occasionally during printing, most service stations have an elastomeric wiper that wipes the printhead surface to remove ink residue, as well as any paper dust or other debris that has collected on the printhead. The wiping action is usually achieved through relative motion of the printhead and wiper, for instance by moving the printhead across the wiper, by moving the wiper across the printhead, or by moving both the printhead and the wiper.
As the inkjet industry investigates new printhead designs, the tendency is toward using permanent or semi-permanent printheads in what is known in the industry as an "off-axis" printer. In an off-axis system, the printheads carry only a small ink supply across the printzone, with this supply being replenished through tubing that delivers ink from an "off-axis" stationary reservoir placed at a remote stationary location within the printer. Since these permanent or semi-permanent printheads carry only a small ink supply, they may be physically more narrow than their predecessors, the replaceable cartridges. Narrower printheads lead to a narrower printing mechanism, which has a smaller "footprint," so less desktop space is needed to house the printing mechanism during use. Narrower printheads are usually smaller and lighter, so smaller carriages, bearings, and drive motors may be used, leading to a more economical printing unit for consumers.
There are a variety of advantages associated with these off-axis printing systems, but the permanent or semi-permanent nature of the printheads requires special considerations for servicing, particularly when wiping ink residue from the printheads, which must be done without any appreciable wear that could decrease printhead life. Indeed, keeping the nozzle face plate clean for cartridges using pigment-based inks has proven quite challenging. With the earlier dye-based inks, periodically wiping the printhead with an elastomeric wiper was sufficient. Any die-based ink residue on the wiper was removed by a small scraper regions along each side edge of the printhead, which was supplied as a replaceable cartridge so residue build-up over the lifetime of the printer was not an issue. However, with the advent of the pigment-based inks, a secondary operation of cleaning the wiper has become necessary to remove sticky pigment ink residue from the wiper. In the early printers using these pigment based inks, this secondary wiper cleaning operation was accomplished using a rigid plastic scrapper bar. Through relative motion of either the scrapper, the wiper blade, or both, the wiper was scrapped across the rigid scraper bar to remove ink from the surfaces of the wiper blade.
For instance, one earlier cam-operator wiper scraper system first used in the DeskJet.RTM. 850C and 855C models of inkjet printers, sold by the present assignee, the Hewlett-Packard Company of Palo Alto, Calif., required intricate ink wicking channels to draw the liquid portions of the ink away from the main scrapper surface and into an absorbent ink blotter member. Unfortunately, this cam-operated system required many complex parts, which increased the assembly costs as well as the part cost for manufacturing these printers. Another scraper system first sold by the Hewlett-Packard Company as the model 720CDeskJet.RTM. inkjet printer, moved the wipers translationally under a rigid plastic scraper bar. This translational scraping system, while being simpler to manufacture than the earlier cam-operated system, unfortunately required extra horizontal travel distance for the wipers to travel under the scraper bar. The travel distance also included an over-travel component beyond the scraper bar, known as a "wiper bend-over distance." This bend-over distance allowed the flexed wiper to return to an upright position following scraping of the first side of the wiper blade, and before reversing the direction of travel back under the bar to clean the other side of the blade. This extra travel distance then required a larger service station, which contributed to increasing the size of the printer's footprint.
Furthermore, in these earlier wiper scraper systems, the pigment-based ink residue often accumulated on the wiper surface in the form of a paste, which the earlier plastic scrapper was not totally effective in removing. Instead, when encountering this paste-like consistency of ink residue, the plastic scrapper tended to smear the ink on the surface of the wiper as the wiper blade flexed more, rather than removing the residue from the blade surface. Another drawback of the plastic scrapper is the tendency of the wiper blade when moving past the scrapper to flick ink off of the cleaning surface. This ink splatter or flicking action propelled the ink residue to other areas and components inside the printer service station, dirtying any surfaces where it landed. Finally, one of the major annoyances of the earlier wiper scrapers was the aggravating noise generated by the wiper scraping process.
Thus, a need exists for an inkjet printhead wiping system including a wiper cleaner capable that is quiet, avoids paste-like ink build-up on the wiper, minimizes dirty and noisy ink flicking from the blade, and minimizes the footprint size of the printing unit.